Although some research exists on biculturalism and negative adjustment, few studies have examined the mechanisms that account for the positive correlates of biculturalism in U.S. Latino youth. Two competing reverse causal models were tested. Specifically, we examined how biculturalism among 574 U.S. Mexican adolescents (n =296 girls; M = 17.84 years, SD = .46 years) was related to prosocial tendencies and positive self evaluation (i.e., self-esteem and general self-efficacy). The findings yielded supportive evidence for both reverse causal models suggesting that prosocial tendencies may mediate the relations between biculturalism and positive self evaluations, and that positive self evaluations may mediate the relations between biculturalism and prosocial tendencies. The implications of the role of biculturalism for understanding prosocial development and positive self evaluations in U.S. Mexican youth are discussed.